This section provides background information related to the present disclosure, which is not necessarily prior art.
Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to the unsprung portion of tile vehicle. The piston is connected to the sprung portion of the automobile through a piston rod which extends through the pressure tube.
The piston divides the pressure tube into an upper working chamber and a lower working chamber, both of which are filled with hydraulic fluid. Because the piston is able, through valving, to limit the flow of the hydraulic fluid between the upper and lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle. In a dual-tube shock absorber, a fluid reservoir or reserve chamber is defined between the pressure tube and a reserve tube. A base valve is located between the lower working chamber and the reserve chamber to control the flow of fluid between the lower working chamber and the reserve chamber.
For a full-displacement valving system, all rebound damping forces produced by the shock absorber are the result of piston valving, while compression forces are a combination of piston and cylinder-end valving. The greater the degree to which the flow of fluid within the shock absorber is restricted by the piston and/or cylinder end, the greater the damping forces which are generated by the shock absorber. Thus, a highly restricted flow of fluid would produce a firm ride while a less restricted flow of fluid would produce a soft ride.
Shock absorbers have been developed to provide different damping characteristics depending on the speed or acceleration of the piston within the pressure tube. Because of the exponential relationship between pressure drop and flow rate for a fixed orifice, it is a difficult task to obtain a damping force at relatively low piston velocities (i.e., low hydraulic fluid speed), particularly at velocities near zero. Low speed damping force is important to vehicle handling, since most vehicle handling events are controlled by low speed vehicle body velocities.
Various systems for tuning shock absorbers during low speed movement of the piston include a fixed low speed orifice or orifices which provide a defined leak path which is open across the piston for both compression and rebound. While a soft ride is generally preferred during compression, a firm ride is generally preferred during rebound.